Broadband microfabriated ultrasonic transducer and method of fabrication

• US 5,870,351 A
• Filed: 10/29/1996
• Issued: 02/09/1999
• Est. Priority Date: 10/21/1994
• Status: Expired due to Term

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Inventors: Ladabaum, Igal, Khuri-Yakub, Butrus Thomas
• Primary Examiner(s): ELDRED, JOHN W
• Application Number:
  US08/739,446
• Time in Patent Office: 833 Days
• Field of Search: 367/163, 367/174, 381/113, 381/116, 381/174, 381/191
• US Class Current: 367/163
• CPC Class Codes: B06B 1/0292 Electrostatic transducers, e.g. electret-type
• CPC Class Codes: B06B 1/0696 with a plurality of electrodes on both sides
• CPC Class Codes: H02N 1/006 of the gap-closing type H02N1/004 takes precedence

Abstract

A broadband microfabricated ultrasonic transducer which includes a plurality of resonant membranes of different sizes and/or shapes supported above a conductive substrate.

Claims

1. A broadband microfabricated ultrasonic transducer comprising:

a substrate;

a plurality of resonant membranes of different sizes with each size selected for its resonant frequency supported spaced from the substrate by an insulating support;

and means for applying voltages between said membranes and said substrate.

2. A broadband microfabricated transducer as in claim 1 in which the membrane is silicon nitride having a predetermined residual stress.

3. A broadband transducer as in claim 1 in which the insulating support is silicon oxide.

4. A broadband transducer as in claim 1 in which the insulating support is parylene.

5. A transducer array comprising:

a substrate;

a plurality of ultrasonic transducers on said substrate, each of said transducers including a plurality of resonant membranes of different sizes with each size selected to resonate at a selected frequency or frequencies, said membranes each supported spaced from said substrate by an insulating support;

and means for applying voltages between selected membranes and said substrate whereby to focus and/or scan the ultrasonic energy from said plurality of membranes.

6. A broadband microfabricated transducer as in claim 5 in which the membrane is silicon nitride having a predetermined residual stress.

7. A broadband transducer as in claim 5 in which the insulating support is silicon oxide.

8. A broadband transducer as in claim 5 in which the insulating support is parylene.

9. A broadband transducer as in claims 6, 7, or 8 in which the transducers are in a linear array.

10. A broadband transducer as in claims 6, 7, or 8 in which the transducers are in a two dimensional array.

11. A broadband microfabricated ultrasonic transducer comprising:

a conductive semiconductor substrate;

a plurality of silicon nitride membranes of different sizes with each size selected for its resonant frequency, said membranes supported spaced from said substrate at their edges by an insulating support;

and a conductive film formed on the surface of said membranes whereby a voltage can be applied between said membranes and said conductive semiconductor substrate.

12. A broadband transducer as in claim 11 in which the insulating support is silicon oxide.

13. A broadband transducer as in claim 11 in which the insulating support is parylene.

14. A broadband transducer as in claim 11 in which the membranes have areas which range from 300 to 30,000 μ

m² and thicknesses which range from 0.1 to 1 μ

m, and an insulator support thickness which ranges from 0.1 to 2 μ

m.

15. A broadband transducer as in claims 11, 12, 13, or 14 in which the membranes have different shapes.

16. The method of forming a broadband ultrasonic transducer which comprises the steps of:

selecting a semiconductor conductive substrate forming a thin sacrificial insulating layer on one surface of said substrate;

forming a thin silicon nitride layer on the surface of said insulating layer;

forming a number of etchant access holes in said silicon nitride layer, said holes being closely spaced and arranged in patterns each including a plurality of spaced access holes;

etching the sacrificial insulating layer through said access holes for a period of time which etches away the sacrificial material layer to form a membrane at each pattern of holes.